Hello Sathish
What Andrew is stating here is that the cost of the last link that was traversed by a BPDU is added by the receiving switch. Let me clarify using the following diagram:
- A BPDU will be sent from the root bridge (SW1) to SW2. When the root bridge sends this BPDU, it will not add any cost, but will simply send it.
- When SW2 receives this BPDU, it will add the cost of the link between SW1 and SW2. The receiving switch adds the cost.
- As it prepares to forward the BPDU to SW4, that added cost of the link is included in the BPDU, and it sends it along its way.
- SW4 receives the BPDU with only the cost of the link between SW1 and SW2 included. SW4 will add the cost of the link between SW2 and SW4.
This is what Andrew means in his post. Does that make sense?
I hope this has been helpful!
Laz